The generation of symbols for printing or display by selecting predetermined groups of dots from a set matrix of potential dots is a highly developed art. This technique has been used in various forms for telegraph printers, cathode ray tube type computer output terminals, computer line printers and graphics quality photo-composers, to mention a few diverse examples.
The techniques and apparatus employed in xerographic copy devices have been proposed for some time for use in generating original text or pictures directly from electronic signals, rather than from the usual optically projected pre-formed image. An example of one such arrangement is found in U.S. Pat. No. 2,829,025.
A preferred configuration of an original text xerographic printer exposes a page image by progressive columnar page segments that extend parallel to the axis of the xerographic copy drum. This arrangement maximizes the page production speed of the printer by processing pages in the direction of their shorter dimension or width. Certain types of text are normally printed with lines of text that read along the long dimension of the page. An example of this type of text is familiar computer printout sheets.
It is desirable for an optical printer to be able to generate output having lines of text that extend selectively along either the long or short dimension of the page principally by the selection of type font control data that presents character matrix information that is pedetermined according to the desired character orientation. If, for example, printing is normally to occur with lines of text extending along the short dimension of the page, such printing can be controlled by a first type font data bank defining patterns for generating characters in terms of columnar or vertical raster scans or strokes. To produce writing lines extending horizontally along the long dimension of the page, a "rotated font" data bank is provided which defines patterns for generating characters by raster scans extending horizontally or along the writing line of the page. In printing either type of page the paper is fed to the printing machine in an identical manner, the only difference being the character generation control that places the image on the xerographic drum.
Printed material can be classified as having fixed or proportional spacing depending upon whether all characters regardless of their size are allotted the same horizontal spacing or are allotted an amount of horizontal spacing proportional to their size. Proportional spacing provides printing with a prestige appearance and also provides a more compact writing form that is generally found easier to read.